We continue to develop mathematical models of human metabolism and have conducted several validation studies using a variety of published data on the metabolic responses to overfeeding, underfeeding, and isocaloric changes in dietary macronutrients. Our models have been deployed as an online body weight simulator at http://bwsimulator.niddk.nih.gov to help design prospective studies as well as plan and track clinical weight management programs. Our models are being applied to a variety of problems, from calculating the relationship between human weight change and food intake to calculating changes of free-living energy intake using frequent body weight measurements. We have also used our models to help address policy issues such as the likely effect of soda taxes on US obesity prevalence.